Immunotherapy based on a naked monoclonal antibody (mAb), such as rituximab, has emerged as a safe and effective modality for treatment of indolent and aggressive non-Hodgkin's lymphomas (NHL) and chronic lymphocytic leukemias (CLL). Almost half of the patients with indolent lymphomas failed to respond to initial treatment with rituximab. To improve the therapeutic effectiveness, combination therapy with two mAbs against distinct antigens on B-lymphocytes is under active investigation, providing encouraging results in yet small pilot clinical trials. The objectives of this SBIR investigation is to develop a tetravalent bispecific fusion protein derived from two different humanized antibodies against human CD22 and CD20, and to explore the potentials of utilizing this tetravalent bispecific antibody (bsAb) as a "single agent" for treatment of patients with B-cell neoplastia to further improve the efficacy, safety, and convenience of the combination therapy. In Phase I, the fusion bsAb will be engineered by recombinant technology and expressed in a mammalian cell line, and high-level bsAb-producing clones suitable for industrial scale production will be developed. In this preliminary stage of a new drug development, the physical, biochemical, and immunological properties of the recombinant bsAb will be thoroughly characterized. In addition, in vitro and in vivo characteristics of the bsAb against neoplastic B-cells will be evaluated. Phase II will focus on detailed preclinical studies including biodistribution, pharmacokinetic and tumor therapy in animals. The ultimate goal of the Phase II application is to develop a cell line that is optimized for production in bioreactors so that clinical grade material insufficient quantities can be obtained for clinical studies.